This invention relates generally to the detection of voids or particulates in a fluid and more particularly to novel method and apparatus for detecting voids or particulates in a fluid by measuring the attenuation and doppler shift of a diffuse ultrasonic sound field passed through the fluid containing the voids.
The detection of voids in the fluid in pipes or containing vessels such as steam generators is important in various industries where the control of fluid levels and the detection of leaks is crucial. For example, in the nuclear reactor industry, high pressure water is contained in opaque steel pipes which must remain full of water to provide coolant to the reactor core. The presents of voids in the coolant could be an indication of a large leak, a low water level, low water pressure or an over power condition in the reactor core. Also, in large volume chemical processing systems in chemical plants it is sometimes desirable to be able to monitor voids to ensure proper operation. It is thus desirable to have a means to monitor the amount of voids in a pipe or other containing vessel by direct measurement rather than by inference through some other less direct measurement means.
The invention is particularly useful for detecting voids in the liquid metal coolant (e.g., sodium) of a fast breeder reactor. Although sodium has many advantages as a coolant, it is unfortunately opaque and very chemically reactive. When steam in a breeder reactor steam generator leaks into the sodium, the resultant reaction is exothermic and produces hydrogen bubbles and other reaction products. The hydrogen gas may however eventually dissolve in the sodium before the voids can be detected by prior art means of detection.
The principle prior art leak detection technique for detecting water leaks into sodium detects the presents of hydrogen dissolved in sodium. Hydrogen is detected by the diffusion of the hydrogen through a thin nickel membrane immersed in the sodium. This technique is a sensitive detector for steam/water leaks but has several deficiencies. Since the hydrogen detector is immersed in sodium it is not easy to replace and is very costly. This type of hydrogen meter is usually located some distance away from the steam generator/heat exchanger and therefore the sodium must be transported to the detector by sodium flow. At low sodium flow rates and because of hydrogen diffusion time through the nickel membrane, the response time of the hydrogen meter is slow. Finally, the technique does not distinguish leaked hydrogen from extraneous hydrogen which may be present in the system after tube cleaning or during initial operation.
Another prior art means of leak detection is based on the acoustic noise emitted by high pressure water or steam flow as it issues from a small hole or crack. This technique is sensitive to background acoustic noise level changes due to flow noise. Because of this limitation, very high sodium and steam flow rates render this detection means less sensitive.
A prior art method to detect voids and particulates in the flow stream of the outlet line of a steam generator has been proposed which detects back scattering of an ultrasonic beam due to the flow of voids passed the outlet. However, because of high temperatures in the sodium of the steam generator/heat exchanger some of the voids and particulates may dissolve before reaching the outlet line. Also at low sodium flow rates, the voids may not be entrained in the sodum flow. Consequently it is desirable to have a detector that is rapid, nonintrusive, low cost, easily replaceable and reliable.
It is accordingly an object of this invention to provide an improved method and apparatus to detect voids and particulates in pipes as well as complex structures such as steam generators and heat exchangers.
It is another object of the present invention to provide a method and apparatus that detects voids in the fluid in a steam generator regardless of the fluid flow rates.
It is yet another object of the invention to provide an improved method and apparatus to detect voids and particulates in a fluid by detecting attenuation of an ultrasonic signal coupled into the fluid.
It is yet another object of the invention to provide a novel method and apparatus for improving the safety of operation of a steam generator by means of cost effective, reliable and rapid detection of leaks.
Briefly, according to the foregoing and other objects and acording to one embodiment of the invention, apparatus for detecting voids and particulates in a fluid within a containing means is provided comprising first transducer means coupled to a first location on the containing means for transmitting a diffuse ultrasonic sound field of predetermined frequency into the fluid. In addition, second transducer means is coupled to a second location on the containing means for receiving a portion of the transmitted sound field and generating an electrical signal representative of the received sound field. A signal processing means coupled to the second transducer means is provided for processing the electrical signals to determine the presence of voids and particulates responsive to attenuation of the sound field transmitted through the fluid .